Semiconductor laser device and method of fabricating the same

ABSTRACT

A semiconductor laser device capable of reducing the threshold current and improving luminous efficiency and a method of fabricating the same are obtained. This semiconductor laser device comprises a semiconductor substrate having a principal surface and a semiconductor element layer, formed on the principal surface of the semiconductor substrate, having a principal surface substantially inclined with respect to the principal surface of the semiconductor substrate and including an emission layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor laser device and amethod of fabricating the same, and more particularly, it relates to asemiconductor laser device including a semiconductor element layerhaving an emission layer and a method of fabricating the same.

2. Description of the Background Art

A semiconductor laser device including a semiconductor element layerhaving an emission layer is known in general, as disclosed in JapanesePatent Laying-Open No. 2004-327655, for example. The aforementionedJapanese Patent Laying-Open No. 2004-327655 discloses a nitridesemiconductor laser device prepared by growing a nitride semiconductorlayer (semiconductor element layer) including an emission layer on thesurface (principal surface) of a nitride semiconductor substrate havinga dislocation concentration region and a low dislocation region in astate inclined by 0.3° to 0.7° with respect to the crystal orientationof the nitride semiconductor substrate. In this semiconductor laserdevice, the nitride semiconductor layer is grown in the state inclinedby 0.3° to 0.7° with respect to the crystal orientation of the nitridesemiconductor substrate so that the surface of the nitride semiconductorlayer is parallel (planar) to the surface of the nitride semiconductorsubstrate, whereby dislocations (defects) in the nitride semiconductorlayer propagate perpendicularly to the surface of the nitridesemiconductor substrate. In the process of growing the nitridesemiconductor layer, therefore, dislocations in a portion of the nitridesemiconductor layer located immediately above the dislocationconcentration region of the nitride semiconductor substrate can beinhibited from propagation into another portion of the nitridesemiconductor layer located immediately above the low dislocation regionof the nitride semiconductor substrate. Consequently, the number ofdislocations can be inhibited from increase in the portion of thenitride semiconductor layer located immediately above the lowdislocation region of the nitride semiconductor substrate.

In the nitride semiconductor laser device according to theaforementioned Japanese Patent Laying-Open No. 2004-327655, however,dislocations of the nitride semiconductor layer propagateperpendicularly to the surface of the nitride semiconductor substrate,whereby dislocations of the low dislocation region of the nitridesemiconductor substrate also propagate toward the surface of the portionof the nitride semiconductor layer grown immediately above the lowdislocation region. Therefore, it is difficult to further reduce thenumber of dislocations on the surface of the nitride semiconductorlayer, and hence it is also difficult to further reduce the number ofdislocations in the nitride semiconductor layer including the emissionlayer. Thus, light absorption by dislocations is so hard to reduce thatit is difficult to further improve the luminous efficiency. Further, itis difficult to further reduce the number of nonradiative centers formedin the emission layer since it is difficult to further reduce the numberof dislocations in the emission layer as described above. Thenonradiative centers, which are levels where carriers recombine withoutemitting light, formed in the emission layer increase the thresholdcurrent. Thus, it is difficult to further reduce the threshold current.

SUMMARY OF THE INVENTION

The present invention has been proposed in order to solve theaforementioned problems, and an object of the present invention is toprovide a semiconductor laser device capable of reducing the thresholdcurrent and improving luminous efficiency and a method of fabricatingthe same.

In order to attain the aforementioned object, a semiconductor laserdevice according to a first aspect of the present invention comprises asemiconductor substrate having a principal surface, a semiconductorelement layer, formed on the principal surface of the semiconductorsubstrate, having a principal surface substantially inclined withrespect to the principal surface of the semiconductor substrate andincluding an emission layer and a growth inhibiting portion arranged ona prescribed region of the principal surface of the semiconductorsubstrate, and the growth inhibiting portion includes a defectconcentration region.

In the semiconductor laser device according to the first aspect, ashereinabove described, the semiconductor element layer having theprincipal surface substantially inclined with respect to the principalsurface of the semiconductor substrate and including the emission layeris so provided that the same can be grown with the principal surfaceinclined with respect to the principal surface of the semiconductorsubstrate, whereby the semiconductor element layer can be grown not onlyin a direction perpendicular to the principal surface of thesemiconductor substrate but also in a direction (horizontal direction)parallel thereto. When defects (dislocations) propagated from theprincipal surface of the semiconductor substrate following growth of thesemiconductor element layer grow on the semiconductor element layer,therefore, the defects of the semiconductor layer can be propagated notonly in the direction perpendicular to the principal surface of thesemiconductor substrate but also in the direction (horizontal direction)parallel thereto, whereby the defects can be further inhibited frompropagation to the principal surface of the semiconductor element layeras compared with a case where the defects of the semiconductor elementlayer are propagated only in the direction perpendicular to theprincipal surface of the semiconductor substrate. Thus, formation ofdefects on the principal surface of the semiconductor element layer canbe further suppressed, whereby light absorption by defects can befurther suppressed. Consequently, luminous efficiency can be furtherimproved. Further, formation of defects on the principal surface of thesemiconductor element layer can be further suppressed as describedabove, whereby the number of nonradiative centers formed in the emissionlayer can be further reduced. Consequently, the threshold current can befurther reduced.

In addition, the growth inhibiting portion arranged on the prescribedregion of the principal surface of the semiconductor substrate is soprovided that the growth inhibiting portion can be prevented fromdeposition of film forming species in growth of the semiconductorelement layer, whereby the concentration of film forming species can beincreased in a portion of the semiconductor element layer close to thegrowth inhibiting portion. Thus, the film forming species can so easilydeposit on the portion of the semiconductor element layer close to thegrowth inhibiting portion that this portion can be rendered easier togrow as compared with the remaining portion of the semiconductor elementlayer. Consequently, the portion of the semiconductor element layerclose to the growth inhibiting portion and the remaining portion thereofcan be formed with different thicknesses, whereby the semiconductorelement layer having the principal surface substantially inclined withrespect to the principal surface of the semiconductor substrate can beeasily formed. Further, the growth inhibiting portion is so formed bythe defect concentration region provided on the prescribed region of theprincipal surface of the semiconductor substrate that the semiconductorsubstrate previously formed with the defect concentration region maysimply be employed without separately forming a growth inhibitingportion on the principal surface of the semiconductor substrate, wherebythe fabrication process can be simplified.

In the aforementioned semiconductor laser device according to the firstaspect, the surface of the defect concentration region is preferablyterminated with nitrogen. According to this structure, the surface ofthe growth inhibiting portion including the defect concentration regioncan be easily prevented from deposition of film forming species.

In the aforementioned semiconductor laser device according to the firstaspect, the growth inhibiting portion is preferably so provided as toextend along the <1-100> direction of the semiconductor substrate.According to this structure, a growth component of the semiconductorelement layer in the direction (horizontal direction) parallel to theprincipal surface of the semiconductor substrate can be enlarged ascompared with a case of providing the growth inhibiting portion toextend in a direction along the <11-20> direction of the semiconductorsubstrate, for example, whereby a defect propagation component in thedirection (horizontal direction) parallel to the principal surface ofthe semiconductor substrate can be enlarged. Thus, the defects can befurther effectively inhibited from propagation to the principal surfaceof the semiconductor element layer, whereby formation of defects on theprincipal surface of the semiconductor element layer can be furthereffectively suppressed.

In the aforementioned semiconductor laser device according to the firstaspect, the growth inhibiting portion preferably includes a first growthinhibiting portion and a second growth inhibiting portion arranged onthe principal surface of the semiconductor substrate at a prescribedinterval, and the semiconductor element layer is preferably formedbetween the first growth inhibiting portion and the second growthinhibiting portion while the principal surface of the semiconductorelement layer is preferably concaved. According to this structure,defects of the semiconductor element layer can be easily propagated notonly in the direction perpendicular to the principal surface of thesemiconductor substrate but also in the direction (horizontal direction)parallel thereto in growth of the semiconductor element layer having theconcave principal surface, whereby propagation of defects to theprincipal surface of the semiconductor element layer can be furthersuppressed as compared with a case where the defects of thesemiconductor element layer are propagated only in the directionperpendicular to the principal surface of the semiconductor substrate.

The aforementioned semiconductor laser device provided with thesemiconductor element layer having the concave principal surfacepreferably further comprises a first electrode formed on the principalsurface of the semiconductor element layer and a second electrode formedon the back surface of the semiconductor substrate, so that the firstelectrode of the semiconductor laser device is mounted on a base.According to this structure, a structure including the semiconductorelement layer having a projection portion, functioning as a current pathtoward the emission layer, provided inside the concave principal surfaceof the semiconductor element layer is mounted on the base from the sideof the first electrode formed on the semiconductor element layer,whereby the projection portion located inside the concave principalsurface can be prevented from application of an impact when thesemiconductor laser device is mounted on the base.

The aforementioned semiconductor laser device provided with thesemiconductor element layer having the concave principal surfacepreferably further comprises a projection portion functioning as acurrent path toward the emission layer, and the projection portion ispreferably formed on an inclined region of the principal surface of thesemiconductor element layer. According to this structure, the projectionportion can be easily formed on an inclined plane of the concaveprincipal surface of the semiconductor element layer.

The aforementioned semiconductor laser device having the projectionportion formed on the inclined region of the principal surface of thesemiconductor element layer preferably further comprises a firstelectrode formed on the principal surface of the semiconductor elementlayer and a second electrode formed on the back surface of thesemiconductor substrate, so that the second electrode of thesemiconductor laser device is mounted on a base. According to thisstructure, wire bonding can be performed on the central portion of theupper surface of the first electrode formed on the principal surface ofthe semiconductor element layer while suppressing wire bonding on aportion of the first electrode located above the projection portionformed on the inclined region of the semiconductor element layer in thestate where the second electrode is mounted on the base. Thus, no wirebonding may be performed on an end of the surface of the first electrodein order to prevent wire bonding on the portion of the first electrodelocated above the projection portion, whereby the end of the surface ofthe first electrode can be prevented from chipping resulting from wirebonding.

The aforementioned semiconductor laser device provided with thesemiconductor element layer having the concave principal surfacepreferably further comprises a projection portion functioning as acurrent path toward the emission layer, and the top of the projectionportion is preferably formed on a position lower than the top of thesemiconductor element layer. According to this structure, the projectionportion can be so arranged inside the concave principal surface of thesemiconductor element layer that the same can be further prevented fromapplication of an impact when the semiconductor laser device is mountedon the base or the like.

In the aforementioned semiconductor laser device according to the firstaspect, the misoriented angle of the semiconductor substrate toward the<1-100> direction is preferably at least −0.25° and not more than 0.25°.According to this structure, the inclination of the principal surface ofthe semiconductor element layer can be increased with respect to theprincipal surface of the semiconductor substrate, whereby the defectpropagation component in the direction (horizontal direction) parallelto the principal surface of the semiconductor substrate can be enlargedin growth of the semiconductor element layer. Thus, the defects can befurther effectively inhibited from propagation to the principal surfaceof the semiconductor element layer, whereby formation of defects on theprincipal surface of the semiconductor element layer can be furthersuppressed.

In the aforementioned semiconductor laser device according to the firstaspect, the misoriented angle of the semiconductor substrate toward the<11-20> direction is preferably not more than −0.05° or at least 0.05°.According to this structure, the inclination of the principal surface ofthe semiconductor layer can be increased with respect to the principalsurface of the semiconductor substrate, whereby the principal surface ofthe semiconductor element layer can be inhibited from nonuniformformation of protuberances in growth of the semiconductor element layer.Thus, the emission layer can be inhibited from uneven formation alongprotuberances of the semiconductor element layer, whereby light in theemission layer can be inhibited from outgoing from the upper and lowersurfaces of the emission layer without rectilinear propagation.Consequently, a light confinement effect can be so improved as toimprove luminous efficiency.

A semiconductor laser device according to a second aspect of the presentinvention comprises a semiconductor substrate having a principalsurface, a semiconductor element layer, formed on the principal surfaceof the semiconductor substrate, having a principal surface substantiallyinclined with respect to the principal surface of the semiconductorsubstrate and including an emission layer and a growth inhibitingportion arranged on a prescribed region of the principal surface of thesemiconductor substrate, and the surface of the growth inhibitingportion is terminated with nitrogen.

In the semiconductor laser device according to the second aspect, ashereinabove described, the semiconductor element layer having theprincipal surface substantially inclined with respect to the principalsurface of the semiconductor substrate and including the emission layeris so provided that the same can be grown with the principal surfaceinclined with respect to the principal surface of the semiconductorsubstrate, whereby the semiconductor element layer can be grown not onlyin a direction perpendicular to the principal surface of thesemiconductor substrate but also in a direction (horizontal direction)parallel thereto. When defects (dislocations) propagated from theprincipal surface of the semiconductor substrate following growth of thesemiconductor element layer grow on the semiconductor element layer,therefore, the defects of the semiconductor layer can be propagated notonly in the direction perpendicular to the principal surface of thesemiconductor substrate but also in the direction (horizontal direction)parallel thereto, whereby the defects can be further inhibited frompropagation to the principal surface of the semiconductor element layeras compared with a case where the defects of the semiconductor elementlayer are propagated only in the direction perpendicular to theprincipal surface of the semiconductor substrate. Thus, formation ofdefects on the principal surface of the semiconductor element layer canbe further suppressed, whereby light absorption by defects can befurther suppressed. Consequently, luminous efficiency can be furtherimproved. Further, formation of defects on the principal surface of thesemiconductor element layer can be further suppressed as describedabove, whereby the number of nonradiative centers formed in the emissionlayer can be further reduced. Consequently, the threshold current can befurther reduced.

In addition, the growth inhibiting portion arranged on the prescribedregion of the principal surface of the semiconductor substrate is soprovided that the growth inhibiting portion can be prevented fromdeposition of film forming species in growth of the semiconductorelement layer, whereby the concentration of film forming species can beincreased in a portion of the semiconductor element layer close to thegrowth inhibiting portion. Thus, the film forming species can so easilydeposit on the portion of the semiconductor element layer close to thegrowth inhibiting portion that this portion can be rendered easier togrow as compared with the remaining portion of the semiconductor elementlayer. Consequently, the portion of the semiconductor element layerclose to the growth inhibiting portion and the remaining portion thereofcan be formed with different thicknesses, whereby the semiconductorelement layer having the principal surface substantially inclined withrespect to the principal surface of the semiconductor substrate can beeasily formed. Further, the surface of the growth inhibiting portion isso terminated with nitrogen that the surface of the growth inhibitingportion can be easily prevented from deposition of film forming species.

A method of fabricating a semiconductor laser device according to athird aspect of the present invention comprises steps of preparing asemiconductor substrate provided with at least either a growthinhibiting portion including a defect concentration region or a growthpromoting portion on a prescribed region of the principal surface andgrowing a semiconductor element layer having a principal surfacesubstantially inclined with respect to the principal surface of thesemiconductor substrate and including an emission layer on the principalsurface of the semiconductor substrate through at least either thegrowth inhibiting portion or the growth promoting portion.

In the method of fabricating a semiconductor laser device according tothe third aspect, as hereinabove described, the semiconductor elementlayer having the principal surface substantially inclined with respectto the principal surface of the semiconductor substrate and includingthe emission layer is so formed on the principal surface of thesemiconductor substrate through at least either the growth inhibitingportion or the growth promoting portion that the semiconductor elementlayer can be grown with the principal surface inclined with respect tothe principal surface of the semiconductor substrate, whereby thesemiconductor element layer can be grown not only in a directionperpendicular to the principal surface of the semiconductor substratebut also in a direction (horizontal direction) parallel thereto. Whendefects propagated from the principal surface of the semiconductorsubstrate following growth of the semiconductor element layer grow onthe semiconductor element layer, therefore, the defects of thesemiconductor layer can be propagated not only in the directionperpendicular to the principal surface of the semiconductor substratebut also in the direction (horizontal direction) parallel thereto,whereby the defects can be further inhibited from propagation to theprincipal surface of the semiconductor element layer as compared with acase where the defects of the semiconductor element layer are propagatedonly in the direction perpendicular to the principal surface of thesemiconductor substrate. Thus, formation of defects on the principalsurface of the semiconductor element layer can be further suppressed,whereby light absorption by defects can be further suppressed.Consequently, luminous efficiency can be further improved. Further,formation of defects on the principal surface of the semiconductorelement layer can be further suppressed as described above, whereby thenumber of nonradiative centers formed in the emission layer can befurther reduced. Consequently, the threshold current can be furtherreduced.

In addition, the semiconductor substrate provided with at least thegrowth inhibiting portion or the growth promoting portion on theprescribed region of the principal surface is so employed that thegrowth inhibiting portion can be prevented from deposition of filmforming species when the semiconductor element layer is grown on thesemiconductor substrate provided with the growth inhibiting portion,whereby the concentration of film forming species can be increased in aportion of the semiconductor element layer close to the growthinhibiting portion. Thus, the film forming species can so easily depositon the portion of the semiconductor element layer close to the growthinhibiting portion that this portion can be rendered easier to grow ascompared with the remaining portion of the semiconductor element layer.Consequently, the portion of the semiconductor element layer close tothe growth inhibiting portion and the remaining portion thereof can beformed with different thicknesses, whereby the semiconductor elementlayer having the principal surface substantially inclined with respectto the principal surface of the semiconductor substrate can be easilyformed. When the semiconductor element layer is grown on thesemiconductor substrate provided with the growth promoting portion, onthe other hand, deposition of film forming species on the growthpromoting portion can be so accelerated that the film forming speciescan easily deposit on the portion of the semiconductor element layercorresponding to the growth promoting portion. Thus, the portion of thesemiconductor element layer corresponding to the growth promotingportion can be rendered easier to grow as compared with the remainingportion of the semiconductor element layer. Consequently, the portion ofthe semiconductor element layer corresponding to the growth promotingportion and the remaining portion thereof can be formed with differentthicknesses, whereby the semiconductor element layer having theprincipal surface substantially inclined with respect to the principalsurface of the semiconductor substrate can be easily formed. Further,the semiconductor substrate provided with at least either the growthinhibiting portion including the defect concentration region or thegrowth promoting portion is so employed that no growth inhibitingportion or growth promoting portion may be separately formed on theprincipal surface of the semiconductor substrate, whereby thefabrication process can be simplified.

In the aforementioned method of fabricating a semiconductor laser deviceaccording to the third aspect, the step of preparing the semiconductorsubstrate preferably includes a step of preparing the semiconductorsubstrate in which the surface of the defect concentration region isterminated with nitrogen. According to this structure, the surface ofthe growth inhibiting portion including the defect concentration regioncan be easily prevented from deposition of film forming species.

In the aforementioned method of fabricating a semiconductor laser deviceaccording to the third aspect, the step of preparing the semiconductorsubstrate preferably includes a step of preparing the semiconductorsubstrate including the growth inhibiting portion so provided as toextend along the <1-100> direction of the semiconductor substrate.According to this structure, a growth component of the semiconductorelement layer in the direction (horizontal direction) parallel to theprincipal surface of the semiconductor substrate can be increased ascompared with a case of providing the growth inhibiting portion toextend in a direction along the <11-20> direction of the semiconductorsubstrate, for example, whereby a defect propagation component in thedirection (horizontal direction) parallel to the principal surface ofthe semiconductor substrate can be increased. Thus, the defects can befurther effectively inhibited from propagation to the principal surfaceof the semiconductor element layer, whereby formation of defects on theprincipal surface of the semiconductor element layer can be furthereffectively suppressed.

In the aforementioned method of fabricating a semiconductor laser deviceaccording to the third aspect, the step of preparing the semiconductorsubstrate preferably includes a step of preparing the semiconductorsubstrate on which a first growth inhibiting portion and a second growthinhibiting portion of the growth inhibiting portion are arranged at aprescribed interval, and the step of growing the semiconductor elementlayer preferably includes a step of growing the semiconductor elementlayer having a concave principal surface between the first growthinhibiting portion and the second growth inhibiting portion. Accordingto this structure, defects of the semiconductor element layer can beeasily propagated not only in the direction perpendicular to theprincipal surface of the semiconductor substrate but also in thedirection (horizontal direction) parallel thereto in growth of thesemiconductor element layer having the concave principal surface,whereby propagation of defects to the principal surface of thesemiconductor element layer can be further suppressed as compared with acase where the defects of the semiconductor element layer are propagatedonly in the direction perpendicular to the principal surface of thesemiconductor substrate.

The aforementioned method of fabricating a semiconductor laser deviceaccording to the third aspect preferably further comprises a step offorming a projection portion functioning as a current path toward theemission layer on an inclined region of the principal surface of thesemiconductor element layer. According to this structure, the projectionportion can be easily formed on an inclined plane of the concaveprincipal surface of the semiconductor element layer.

The aforementioned method of fabricating a semiconductor laser deviceaccording to the third aspect preferably further comprises a step offorming the top of a projection portion functioning as a current pathtoward the emission layer on a position lower than the top of thesemiconductor element layer. According to this structure, the projectionportion can be so arranged inside the concave principal surface of thesemiconductor element layer that the same can be further prevented fromapplication of an impact when the semiconductor laser device is mountedon the base or the like.

In the aforementioned method of fabricating a semiconductor laser deviceaccording to the third aspect, the misoriented angle of thesemiconductor substrate toward the <1-100> direction is preferably atleast −0.25° and not more than 0.25°. According to this structure, theinclination of the principal surface of the semiconductor element layercan be increased with respect to the principal surface of thesemiconductor substrate, whereby the defect propagation component in thedirection (horizontal direction) parallel to the principal surface ofthe semiconductor substrate can be increased in growth of thesemiconductor element layer. Thus, the defects can be furthereffectively inhibited from propagation to the principal surface of thesemiconductor element layer, whereby formation of defects on theprincipal surface of the semiconductor element layer can be furthersuppressed.

In the aforementioned method of fabricating a semiconductor laser deviceaccording to the third aspect, the misoriented angle of thesemiconductor substrate toward the <11-20> direction is preferably notmore than −0.05° or at least 0.05°. According to this structure, theinclination of the principal surface of the semiconductor layer can beincreased with respect to the principal surface of the semiconductorlayer, whereby the principal surface of the semiconductor element layercan be inhibited from nonuniform formation of protuberances in growth ofthe semiconductor element layer. Thus, the emission layer can beinhibited from uneven formation along protuberances of the semiconductorelement layer, whereby light in the emission layer can be inhibited fromoutgoing from the upper and lower surfaces of the emission layer.Consequently, a light confinement effect can be so improved as toimprove luminous efficiency.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the structure of a nitride-basedsemiconductor laser device according to a first embodiment of thepresent invention;

FIG. 2 is an enlarged sectional view showing the detailed structure ofan emission layer of the nitride-based semiconductor laser deviceaccording to the first embodiment shown in FIG. 1;

FIGS. 3 and 4 are enlarged sectional views showing the structure of ann-side cladding layer of the nitride-based semiconductor laser deviceaccording to the first embodiment shown in FIG. 1;

FIG. 5 is a fragmented perspective view showing the structure of then-side cladding layer of the nitride-based semiconductor laser deviceaccording to the first embodiment shown in FIG. 1;

FIGS. 6 and 7 are sectional views of the nitride-based semiconductorlaser device according to the first embodiment shown in FIG. 1 mountedon a heat radiator base;

FIGS. 8 to 20 are sectional views for illustrating a process offabricating the nitride-based semiconductor laser device according tothe first embodiment shown in FIG. 1;

FIG. 21 is a sectional view showing the structure of a nitride-basedsemiconductor laser device according to a second embodiment of thepresent invention;

FIG. 22 is an enlarged sectional view showing the detailed structure ofan emission layer of the nitride-based semiconductor laser deviceaccording to the second embodiment show in FIG. 21;

FIGS. 23 and 24 are sectional views showing the structure of an n-sidecladding layer of the nitride-based semiconductor laser device accordingto the second embodiment shown in FIG. 21;

FIG. 25 is a fragmented perspective view showing the structure of then-side cladding layer of the nitride-based semiconductor laser deviceaccording to the second embodiment shown in FIG. 21;

FIGS. 26 and 27 are sectional views of the nitride-based semiconductorlaser device according to the second embodiment shown in FIG. 21 mountedon a heat radiator base;

FIGS. 28 to 40 are sectional views for illustrating a process offabricating the nitride-based semiconductor laser device according tothe second embodiment shown in FIG. 21; and

FIGS. 41 to 43 are graphs showing results of confirmatory experimentsconducted for confirming effects of the nitride-based semiconductorlaser device according to the second embodiment shown in FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are now described with reference tothe drawings.

First Embodiment

FIG. 1 is a sectional view showing the structure of a nitride-basedsemiconductor laser device according to a first embodiment of thepresent invention. FIG. 2 is an enlarged sectional view showing thedetailed structure of an emission layer 4 of the nitride-basedsemiconductor laser device according to the first embodiment shown inFIG. 1. FIGS. 3 to 5 are sectional views for detailedly illustrating thestructure of the nitride-based semiconductor laser device according tothe first embodiment shown in FIG. 1. FIGS. 6 and 7 are sectional viewsshowing the nitride-based semiconductor laser device according to thefirst embodiment shown in FIG. 1 mounted on a heat radiator base(submount) 11. The structure of the nitride-based semiconductor laserdevice according to the first embodiment is now described with referenceto FIGS. 1 to 7.

In the nitride-based semiconductor laser device according to the firstembodiment, SiO₂ films 2 having a thickness of about 0.2 μm and a widthof about 25 μm are arranged on of an n-type GaN substrate 1 havingdefects 1 a (see FIG. 4) on the principal surface thereof at aprescribed interval W1 (about 250 μm), as shown in FIG. 1. The n-typeGaN substrate 1 is an example of the “semiconductor substrate” in thepresent invention, and the SiO₂ films 2 are examples of the “growthinhibiting portion” in the present invention.

According to the first embodiment, the SiO₂ films 2 are formed in astriped manner to extend in the [1-100] direction of the n-type GaNsubstrate 1 (perpendicular to the plane of FIG. 1). According to thefirst embodiment, the cavity direction is identical to the [1-100]direction of the semiconductor substrate. An n-side cladding layer 3 ofn-type AlGaN is formed on a region of the n-type GaN substrate 1 locatedbetween the SiO₂ films 2 and partial regions of the SiO₂ films 2. Then-side cladding layer 3 is an example of the “semiconductor elementlayer” in the present invention.

According to the first embodiment, the principal surface (upper surface)of the n-side cladding layer 3 is concaved. The central portion of then-side cladding layer 3 has a thickness T1 (about 2.3 μm), while sideportions thereof have a thickness T2 (about 3.3 μm). The n-side claddinglayer 3 is so formed that the principal surface of a portion inwardbeyond the ends of the SiO₂ films 2 by W2 (about 100 μm) is inclined byan angle θ1 (about 0.25°) with respect to the principal surface of then-type GaN substrate 1. The surface of a peripheral portion of then-side cladding layer 3 has a prescribed inclination θ2 with respect tothe principal surface of the n-type GaN substrate 1. A joint line 3 a isformed on the central portion of the upper surface of the n-sidecladding layer 3, as shown in FIG. 5. This joint line 3 a is formed ingrowth of the n-side cladding layer 3 due to slight deviation betweenthe heights of surface portions located on the both sides of the jointline 3 a. The joint line 3 a is waved as viewed from above, and extendsalong the extensional direction of the SiO₂ films 2 (cavity direction).Therefore, the central portion of the upper surface of the n-sidecladding layer 3 has unevenness along the cavity direction.

According to the first embodiment, defects (dislocations) 3 b are formedin the n-side cladding layer 3, as shown in FIG. 4. These defects 3 bare continuous with the defects 1 a of the n-type GaN substrate 1. Thedefects 3 b formed in the side portions of the n-side cladding layer 3are bent outward, not to reach the upper surface of the n-side claddinglayer 3. Further, the defects 3 b formed in noncentral portions inwardbeyond the side portions of the n-side cladding layer 3 are bent inward(toward the central portion), not to reach the surface of the n-sidecladding layer 3 b. On the other hand, the defects 3 b formed in thecentral portion of the n-side cladding layer 3 reach the surface of then-side cladding layer 3.

The emission layer 4 is formed on the n-side cladding layer 3 to coverthe n-side cladding layer 3, as shown in FIG. 1. This emission layer 4is an example of the “semiconductor element layer” in the presentinvention. The emission layer 4 is constituted of an active layer 4 a ofInGaN having a thickness of about 0.07 μm, a light guide layer 4 b ofInGaN having a thickness of about 0.1 μm and a cap layer 4 c of AlGaNhaving a thickness of about 0.02 μm, as shown in FIG. 2. The activelayer 4 a has a multiple quantum well (MQW) structure obtained byalternately stacking three well layers 4 d of InGaN each having athickness of about 0.003 μm and three barrier layers 4 e of InGaN eachhaving a thickness of about 0.02 μm, as shown in FIG. 2. A p-sidecladding layer 5 of AlGaN having a thickness of about 0.25 μm is formedon the emission layer 4 to cover the emission layer 4, as shown inFIG. 1. This p-side cladding layer 5 is an example of the “semiconductorelement layer” in the present invention. The p-side cladding layer 5includes a striped (slender) jut portion 5 a having a width of about 1.5μm and extending in the cavity direction (perpendicular to the plane ofFIG. 1) and remaining planar portions. A contact layer 6 of InGaN havinga thickness of about 0.003 μm is formed on the jut portion 5 a of thep-side cladding layer 5. The contact layer 6 is an example of the“semiconductor element layer” in the present invention. The jut portion5 a of the p-side cladding layer 5 and the contact layer 6 constitute aridge portion 15 functioning as a current path toward the emission layer4. The ridge portion 15 is an example of the “projection portion” in thepresent invention. According to the first embodiment, the thicknesses ofthe semiconductor element layers are represented by those correspondingto the position formed with the ridge portion 15.

According to the first embodiment, the top of the ridge portion 15 isarranged on a position lower than the tops 5 b of the side surfaces ofthe p-side cladding layer 5. Further, the ridge portion 15 is formed ona portion inward beyond the end of one of the SiO₂ films 2 by W2 (about100 μm). In other words, the ridge portion 15 is formed on a noncentralinclined plane of the concave principal surface of the p-side claddinglayer 5 having an angle θ1 (about 0.25°). Thus, the ridge portion 15 canbe formed on a portion of the n-side cladding layer 3 out of the unevenportion along the joint line 3 a, thereby preventing a portion of theemission layer 4 close to the ridge portion 15 from unevenness.Therefore, light in the emission layer 4 can be inhibited from outgoingfrom the upper and lower surfaces of the emission layer 4 withoutrectilinear propagation, whereby a light confinement effect can beimproved. Consequently, luminous efficiency can be improved.

A p-side ohmic electrode 7 is formed on the contact layer 6. This p-sideohmic electrode 7 is constituted of a Pt layer (not shown) having athickness of about 0.001 μm and a Pd layer (not shown) having athickness of about 0.01 μm, in ascending order from the side closer tothe contact layer 6. An SiO₂ film (current blocking layer) 8 having athickness of about 0.2 μm is formed to cover the planar portions of thep-side cladding layer 5 and the side surfaces of the contact layer 6 andthe p-side ohmic electrode 7. A pad electrode 9 is formed on a partialregion of the SiO₂ film 8 and the p-side ohmic electrode 7, to be incontact with the p-side ohmic electrode 7. This pad electrode 9 is anexample of the “first electrode” in the present invention. The padelectrode 9 is constituted of a Ti layer (not shown) having a thicknessof about 0.1 μm, a Pd layer (not shown) having a thickness of about 0.2μm and an Au layer (not shown) having a thickness of about 3 μm inascending order from the side closer to the p-side ohmic electrode 7.The height H1 (see FIG. 1) of the portion located between the uppersurface of the pad electrode 9 and the lower surface of the n-type GaNsubstrate 1 is set to about 100 μm.

An n-side ohmic electrode 10 is formed on a prescribed region of theback surface of the n-type GaN substrate 1. This n-side ohmic electrode10 is an example of the “second electrode” in the present invention. Then-side ohmic electrode 10 is constituted of an Al layer (not shown)having a thickness of about 0.006 μm, a Pd layer (not shown) having athickness of about 0.01 μm and an Au layer (not shown) having athickness of about 0.3 μm in descending order from the side closer tothe n-side GaN substrate 1.

The nitride-based semiconductor laser device is mounted on the heatradiator base (submount) 11 in a junction-up state shown in FIG. 6 or ajunction-down state shown in FIG. 7. The heat radiator base 11 is anexample of the “base” in the present invention. More specifically, then-side ohmic electrode 10 is mounted on the heat radiator base 11through a junction layer 12 of solder or the like while a wire 13 a isbonded to the upper surface of the pad electrode 9 in the junction-upstate, as shown in FIG. 6. In this case, the wire 13 a can be bonded tothe central portion of the upper surface of the pad electrode 9 formedon the principal surface of the n-side cladding layer 3 whilesuppressing wire bonding on a portion of the pad electrode 9 locatedabove the ridge portion 15 formed on the noncentral portion of theprincipal surface of the n-side cladding layer 3 in the state where then-side ohmic electrode 10 is mounted on the heat radiator base 11.Therefore, no wire bonding may be performed on the ends of the surfaceof the pad electrode 9, in order to prevent the portion of the padelectrode 9 located above the ridge portion 15 from wire bonding. Thus,the ends of the surface of the pad electrode 9 can be inhibited fromchipping in bonding of the wire 13 a. In the junction-down state, on theother hand, the pad electrode 9 is mounted on the heat radiator base 11through a junction layer 14 of solder or the like while a wire 13 b isbonded to the n-side ohmic electrode 10, as shown in FIG. 7. In thiscase, the device including the n-side cladding layer 3 having the ridgeportion 15 arranged inside the concave principal surface is mounted onthe heat radiator base 11 from the side of the pad electrode 9 formed onthe n-side cladding layer 3, whereby the ridge portion 15 located insidethe concave principal surface can be prevented from application of animpact when the device is mounted on the heat radiator base 11.

According to the first embodiment, as hereinabove described, the n-sidecladding layer 3 having the principal surface substantially inclinedwith respect to the principal surface of the n-type GaN substrate 1 withthe emission layer 4 formed on the principal surface is so provided thatthe same can be grown with the principal surface inclined with respectto the principal surface of the n-type GaN substrate 1, whereby then-side cladding layer 3 can be grown not only in a direction Yperpendicular to the principal surface of the n-type GaN substrate 1 butalso in a direction X (horizontal direction) parallel thereto. When thedefects (dislocations) 3 b propagated from the principal surface of then-type GaN substrate 1 following growth of the n-side cladding layer 3grow on the n-side cladding layer 3, therefore, the defects 3 b of then-side cladding layer 3 can be propagated not only in the direction Yperpendicular to the principal surface of the n-type GaN substrate 1 butalso in the direction X (horizontal direction) parallel thereto, wherebythe defects 3 b can be further inhibited from propagation to theprincipal surface of the n-side cladding layer 3 as compared with a casewhere the defects 3 b of the n-side cladding layer 3 are propagated onlyin the direction Y perpendicular to the principal surface of the n-typeGaN substrate 1. Thus, formation of the defects 3 b on the principalsurface of the n-side cladding layer 3 can be further suppressed,whereby light absorption by the defects 3 b can be further suppressed.Further, propagation of the defects 3 b to the emission layer 4 and thep-side cladding layer 5 can be so suppressed that light absorption bythe defects 3 b can be suppressed. Consequently, luminous efficiency canbe further improved. In addition, formation of the defects 3 b on theprincipal surface of the n-side cladding layer 3 can be furthersuppressed as described above, whereby the number of nonradiativecenters formed in the emission layer 4 can be further reduced.Consequently, the threshold current can be further reduced.

According to the first embodiment, the principal surface of the n-sidecladding layer 3 is concaved and the ridge portion 15 is formed on theinclined plane of the concave principal surface of the n-side claddinglayer 3 so that the ridge portion 15 can be provided on the inclinedplane of the concave principal surface of the n-side cladding layer 3having a small number of defects 3 b due to a large horizontal growthcomponent, whereby the number of defects 3 b can be reduced on a portionof the emission layer 4 around the ridge portion 15. Thus, the luminousefficiency of the emission layer 4 can be further improved.

FIGS. 8 to 20 are sectional views for illustrating a process offabricating the nitride-based semiconductor laser device according tothe first embodiment shown in FIG. 1. The process of fabricating thenitride-based semiconductor laser device according to the firstembodiment is now described with reference to FIGS. 1, 2, 4, 5 and 8 to20.

As shown in FIG. 8, the SiO₂ films 2 having the thickness of about 0.2μm and a width W3 (about 50 μm) are formed on the n-type GaN substrate 1in a cycle W4 (about 300 μm) are prepared. At this time, the SiO₂ films2 are formed in the striped manner to extend in a direction along the[1-100] direction of the n-type GaN substrate 1. As shown in FIG. 9, then-side cladding layer 3 of n-type AlGaN is grown on the n-type GaNsubstrate 1 by metal organic chemical vapor deposition (MOCVD), so thatthe central portion thereof has the thickness T1 (about 2.3 μm) (seeFIG. 1). In order to grow the n-side cladding layer 3, the temperature,the gas pressure and the growth rate are set to about 1100° C., about5.74 Pa and about 0.32 nm/s respectively, while the gas flow rates areset to about 11 sccm for trimethylgallium (TMG), about 5 sccm fortrimethylaluminum (TMA), about 6 slm for NH₃ and about 20 sccm for GeH₄respectively.

In this case, growth species A are inhibited from depositing on thesurfaces of the SiO₂ films 2 serving as growth inhibiting portionsaccording to the first embodiment as shown in FIG. 18, whereby theconcentration of the growth species A is increased in portions of then-side cladding layer 3 close to the SiO₂ films 2. Thus, the growthspecies A so easily deposit on the portions of the n-side cladding layer3 close to the SiO₂ films 2 that these portions are easier to grow ascompared with the central portion of the n-side cladding layer 3.Consequently, the central portion of the n-side cladding layer 3 and theportions thereof close to the SiO₂ films 2 are formed with differentthicknesses, whereby the principal surface of the n-side cladding layer3 is substantially inclined with respect to the principal surface of then-type GaN substrate 1. In this case, the n-side cladding layer 3 isformed only on the principal surface of the n-type GaN substrate 1 in aninitial growth stage, as shown in FIG. 18. Growth of the n-side claddinglayer 3 so progresses that the side portions of the n-side claddinglayer 3 have the prescribed inclination θ2, as shown in FIG. 19.Thereafter growth of the n-side cladding layer 3 further progresses sothat the n-side cladding layer 3 is formed up to the upper surfaces ofthe SiO₂ films 2 while holding the prescribed inclination θ2 on the sideportions thereof.

According to the first embodiment, the defects 3 b are formed in then-side cladding layer 3 in the growth process thereof continuously withthe defects 1 a of the n-type GaN substrate 1, as shown in FIG. 20. Inthis case, the n-side cladding layer 3 grows not only in the direction Yperpendicular to the principal surface of the n-type GaN substrate 1 butalso in the direction X parallel thereto, as disclosed in literature(“Defect Structure in Selectively Grown GaN Films with Low ThreadingDislocation Density”, Sakai et al., Appl. Phys. Lett. 71, pp. 2259-2261,20 Oct. 1997), for example. More specifically, the side portions of then-side cladding layer 3 outwardly grow from the state shown in FIG. 20,as shown in FIG. 4. Further, the noncentral portions of the n-sidecladding layer 3 inward beyond the side portions inwardly grow (towardthe central portion). The joint line 3 a (see FIG. 5) is formed on thecentral portion of the n-side cladding layer 3. The defects 3 b formedin the noncentral portions of the n-side cladding layer 3 are bent inthe horizontal direction X to disappear, as shown in FIG. 4. At thecentral portion of the n-side cladding layer 3, on the other hand, thedefects 3 b propagate to the surface of the n-side cladding layer 3without disappearing, due to a small growth component in the direction Xparallel to the surface of the n-type GaN substrate 1.

As shown in FIG. 9, the emission layer 4 is grown to cover the n-sidecladding layer 3. In order to grow this emission layer 4, the three welllayers 4 d of InGaN each having the thickness of about 0.003 μm and thethree barrier layers 4 e of InGaN each having the thickness of about0.02 μm are alternately grown as shown in FIG. 2 for forming amultilayer film of the MQW structure, thereby forming the active layer 4a constituted of the MQW structure multilayer film formed by the threewell layers 4 d and the three barrier layers 4 e. In order to grow thisactive layer 4 a, the temperature, the gas pressure and the growth rateare set to about 850° C., about 5.74 Pa and about 0.11 nm/srespectively, while the gas flow rates are set to about 75 sccm fortriethylgallium (TEG), about 230 sccm for trimethylindium (TMI) andabout 8 slm for NH₃ respectively. Then, the light guide layer 4 b ofInGaN having the thickness of about 0.1 μm and the cap layer 4 c ofAlGaN having the thickness of about 0.02 μm are grown on the activelayer 4 a of InGaN having the thickness of about 0.07 μm. In order togrow the light guide layer 4 b, the temperature, the gas pressure andthe growth rate are set to about 860° C., about 5.74 Pa and about 0.11nm/s respectively, while the gas flow rates are set to about 75 sccm forTEG, about 30 sccm for TMI and about 8 slm for NH₃ respectively. Inorder to grow the cap layer 4 c, further, the temperature, the gaspressure and the growth rate are set to about 1100° C., about 5.74 Paand about 0.32 nm/s respectively, while the gas flow rates are set toabout 20 sccm for TMG, about 250 sccm for TMA and about 8 slm for NH₃respectively. Thereafter the p-side cladding layer 5 of AlGaN having athickness of about 0.4 μm is grown on the surface of the emission layer4. In order to grow the p-side cladding layer 5, the temperature, thegas pressure and the growth rate are set to about 1100° C., about 5.74Pa and about 0.35 nm/s respectively, while the gas flow rates are set toabout 11 sccm for TMG, about 5 sccm for TMA, about 6 slm for NH₃ andabout 20 sccm for bis(cyclopentadienyl)magnesium (Cp₂Mg) respectively.Thereafter the contact layer 6 of InGaN having the thickness of about0.003 μm is grown on the surface of the p-side cladding layer 5. Inorder to grow the contact layer 6, the temperature, the gas pressure andthe growth rate are set to about 850° C., about 5.74 Pa and about 0.11nm/s respectively, while the gas flow rates are set to about 75 sccm forTEG, about 100 sccm for TMI and about 8 slm for NH₃ respectively.

As shown in FIG. 10, the Pt layer (not shown) having the thickness ofabout 0.001 μm and the Pd layer (not shown) having the thickness ofabout 0.01 μm are thereafter successively formed on the contact layer 6by vacuum evaporation or the like, thereby forming the p-side ohmicelectrode 7 consisting of the Pt and Pd layers. An SiO₂ film 16 having athickness of about 0.24 μm is formed on the surface of the p-side ohmicelectrode 7 by plasma CVD. A striped resist film 17, having a width ofabout 1.5 μm, extending in the cavity direction is formed on a region(inward beyond the end of one of the SiO₂ films 2 by W2 (about 100 μm))of the p-side ohmic electrode 7 for forming the ridge portion 15 (seeFIG. 1).

As shown in FIG. 11, prescribed regions of the SiO₂ film 16 and thep-side ohmic electrode 7 are removed by reactive ion etching (RIE) withCF₄ gas through the resist film 17 serving as a mask. Thereafter theresist film 17 is removed.

As shown in FIG. 12, prescribed regions between the upper surface of thecontact layer 6 and an intermediate portion of the p-side cladding layer5 (having a depth of about 150 nm from the upper surface of the activelayer 4 a) are removed by RIE with Cl₂ gas through the SiO₂ film 16serving as a mask, thereby forming the ridge portion 15 consisting ofthe jut portion 5 a of the p-side cladding layer 5 and the contact layer6. Thereafter the SiO₂ film 16 is removed.

As shown in FIG. 13, the SiO₂ film 8 having the thickness of about 0.2μm is formed by plasma CVD to cover the overall surface. A resist film18 is applied to cover the SiO₂ film 8. Then, the resist film 18 ispartially removed by oxygen plasma etching, to expose a portion of theSiO₂ film 8 located on the ridge portion 15. Thereafter the portion ofthe SiO₂ film 8 located on the ridge portion 15 is removed by RIE withCF₄ gas through the resist film 18 serving as a mask, thereby formingthe current blocking layer consisting of the SiO₂ film 8 having a shapeshown in FIG. 14. Thereafter the resist film 18 is removed.

As shown in FIG. 15, resist films 19 are formed on regions other thanthat for forming the pad electrode 9, and the Ti layer (not shown)having the thickness of about 0.1 μm, the Pd layer (not shown) havingthe thickness of about 0.2 μm and the Au layer (not shown) having thethickness of about 3 μm are formed in this order by vacuum evaporationor the like, thereby forming the pad electrode 9. Thereafter the resistfilms 19 are removed, thereby forming the pad electrode 9 constituted ofthe patterned Ti, Pd and Au layers as shown in FIG. 16. Thereafter thelower surface of the n-type GaN substrate 1 is polished, so that theheight H1 (see FIG. 1) of the portion located between the upper surfaceof the pad electrode 9 and the lower surface of the n-type GaN substrate1 is about 100 μm.

As shown in FIG. 17, the Al layer (not shown) having the thickness ofabout 0.006 μm, the Pd layer (not shown) having the thickness of about0.01 μm and the Au layer (not shown) having the thickness of about 0.3μm are formed in this order on the prescribed region of the back surfaceof the n-type GaN substrate 1 by vacuum evaporation or the like, therebyforming the n-side ohmic electrode 10 consisting of the Al, Pd and Aulayers. The n-type GaN substrate 1 is divided into each device, therebyforming the nitride-based semiconductor laser device according to thefirst embodiment shown in FIG. 1.

An experiment conducted in relation to propagation of defects 3 b inn-type GaN substrates 1 formed with SiO₂ films 2 in different directionswith respect to the n-type GaN substrates 1 is now described. In thisexperiment, the n-type GaN substrates 1 were formed with the SiO₂ films2 extending in directions along the [1-100] and [11-20] directionsrespectively, and n-side cladding layers 3 were grown on the surfaces ofthese n-type GaN substrates 1. Consequently, it has been proved that apropagation component for defects 3 b in a direction parallel to thesurface of the n-type GaN substrate 1 formed with the SiO₂ films 2extending in the direction along the [1-100] direction is more increasedand the defects 3 b on the surface of the n-side cladding layer 3 aremore easily disappear as compared with the n-type GaN substrate 1 formedwith the SiO₂ films 2 extending in the direction along the [11-20]direction. Thus, it is preferable to employ the n-type GaN substrate 1formed with the SiO₂ films 2 extending in the direction along the[1-100] direction.

Second Embodiment

FIG. 21 is a sectional view showing the structure of a nitride-basedsemiconductor laser device according to a second embodiment of thepresent invention. FIG. 22 is an enlarged sectional view showing thedetailed structure of an emission layer 23 of the nitride-basedsemiconductor laser device according to the second embodiment shown inFIG. 21. FIGS. 23 to 25 are sectional views for detailedly illustratingthe structure of the nitride-based semiconductor laser device accordingto the second embodiment shown in FIG. 21. FIGS. 26 and 27 are sectionalviews showing the nitride-based semiconductor laser device according tothe second embodiment shown in FIG. 21 mounted on a heat radiator base(submount) 31. The structure of the nitride-based semiconductor laserdevice according to the second embodiment is now described withreference to FIGS. 21 to 27.

In the nitride-based semiconductor laser device according to the secondembodiment, an n-type GaN substrate 21 includes defect concentrationregions 21 a formed on ends of the n-type GaN substrate 21 withprincipal surfaces terminated with nitrogen and a low defect densityregion 21 b arranged between the defect concentration regions 21 a. Then-type GaN substrate 21 is an example of the “semiconductor substrate”in the present invention, and the defect concentration regions 21 a areexamples of the “growth inhibiting portion” in the present invention.The defect concentration regions 21 a having a width of about 25 μm arearranged at a prescribed interval W5 (about 350 μm).

According to the second embodiment, the defect concentration regions 21a are formed in a striped manner to extend in the [1-100] direction ofthe n-type GaN substrate 21 (perpendicular to the plane of FIG. 21).According to the second embodiment, the cavity direction is identical tothe [1-100] direction of the semiconductor substrate. An n-side claddinglayer 22 of n-type AlGaN is formed on the low defect density region 21 band partial regions of the defect concentration regions 21 a. The n-sidecladding layer 22 is an example of the “semiconductor element layer” inthe present invention.

According to the second embodiment, the principal surface (uppersurface) of the n-side cladding layer 22 is concaved. The centralportion of the n-side cladding layer 22 has a thickness T3 (about 2.3μm), while side portions thereof have a thickness T4 (about 2.8 μm). Then-side cladding layer 22 is so formed that the principal surface of aportion inward beyond the end of one of the defect concentration regions21 a by W6 (about 130 μm) is inclined by an angle θ3 (about 0.2°) withrespect to the principal surface of the n-type GaN substrate 21. Thesurface of a peripheral portion of the n-side cladding layer 22 has aprescribed inclination θ4 with respect to the principal surface of then-type GaN substrate 21. A joint line 22 a is formed on the centralportion of the upper surface of the n-side cladding layer 22, as shownin FIG. 25. This joint line 22 a is formed in growth of the n-sidecladding layer 22 due to slight deviation between the heights of surfaceportions located on both sides of the joint line 22 a. The joint line 22a is waved as viewed from above, and extends along the extensionaldirection of the defect concentration regions 21 a (cavity direction).Therefore, the central portion of the upper surface of the n-sidecladding layer 22 has unevenness along the cavity direction.

According to the second embodiment, defects (dislocations) 22 b areformed in the n-side cladding layer 22, as shown in FIG. 24. Thesedefects 22 b are continuous with the defects 21 c of the surfaces of thedefect concentration regions 21 a and the low defect density region 21 bof the n-type GaN substrate 21. The defects 22 b formed in the sideportions of the n-side cladding layer 22 are bent outward. Further, thedefects 22 b formed in noncentral portions inward beyond the sideportions of the n-side cladding layer 22 are bent inward (toward thecentral portion), not to reach the surface of the n-side cladding layer22. On the other hand, the defects 22 b formed in the central portion ofthe n-side cladding layer 22 reach the surface of the n-side claddinglayer 22.

The emission layer 23 is formed on the n-side cladding layer 22 to coverthe n-side cladding layer 22, as shown in FIG. 21. This emission layer23 is an example of the “semiconductor element layer” in the presentinvention. The emission layer 23 is constituted of an active layer 23 aof InGaN having a thickness of about 0.07 μm, a light guide layer 23 bof InGaN having a thickness of about 0.1 μm and a cap layer 23 c ofAlGaN having a thickness of about 0.02 μm, as shown in FIG. 22. Theactive layer 23 a has an MQW structure obtained by alternately stackingthree well layers 23 d of InGaN each having a thickness of about 0.003μm and three barrier layers 23 e of InGaN each having a thickness ofabout 0.02 μm. A p-side cladding layer 24 of AlGaN having a thickness ofabout 0.25 μm is formed on the emission layer 23 to cover the emissionlayer 23, as shown in FIG. 21. This p-side cladding layer 24 is anexample of the “semiconductor element layer” in the present invention.The p-side cladding layer 24 includes a striped (slender) jut portion 24a having a width of about 1.5 μm and extending in the cavity direction(perpendicular to the plane of FIG. 21) and remaining planar portions. Acontact layer 25 of InGaN having a thickness of about 0.003 μm is formedon the jut portion 24 a of the p-side cladding layer 24. The contactlayer 25 is an example of the “semiconductor element layer” in thepresent invention. The jut portion 24 a of the p-side cladding layer 24and the contact layer 25 constitute a ridge portion 35 functioning as acurrent path toward the emission layer 23. The ridge portion 35 is anexample of the “projection portion” in the present invention. Accordingto the second embodiment, the thicknesses of the semiconductor elementlayers are represented by those corresponding to the position formedwith the ridge portion 35.

According to the second embodiment, the top of the ridge portion 35 isarranged on a position lower than the tops 24 b of the side surfaces ofthe p-side cladding layer 24. Further, the ridge portion 35 is formed onthe portion inward beyond the end of one of the defect concentrationregions 21 a by W6 (about 130 μm). In other words, the ridge portion 35is formed on a noncentral inclined plane of the concave principalsurface of the p-side cladding layer 24 having an angle θ3 (about 0.2°).Thus, the ridge portion 35 can be formed on a portion of the n-sidecladding layer 3 out of the uneven portion along the joint line 22 a,thereby preventing a portion of the emission layer 23 close to the ridgeportion 35 from unevenness. Therefore, light in the emission layer 23can be inhibited from outgoing from the upper and lower surfaces of theemission layer 23 without rectilinear propagation, whereby a lightconfinement effect can be improved. Consequently, luminous efficiencycan be improved.

A p-side ohmic electrode 26 is formed on the contact layer 25. Thisp-side ohmic electrode 26 is constituted of a Pt layer (not shown)having a thickness of about 0.001 μm and a Pd layer (not shown) having athickness of about 0.01 μm, in ascending order from the side closer tothe contact layer 25. An SiO₂ film (current blocking layer) 27 having athickness of about 0.2 μm is formed to cover the planar portions of thep-side cladding layer 24 and the side surfaces of the contact layer 25and the p-side ohmic electrode 26. A pad electrode 28 is formed on apartial region of the SiO₂ film 27 and the p-side ohmic electrode 26, tobe in contact with the p-side ohmic electrode 26. This pad electrode 28is an example of the “first electrode” in the present invention. The padelectrode 28 is constituted of a Ti layer (not shown) having a thicknessof about 0.1 μm, a Pd layer (not shown) having a thickness of about 0.2μm and an Au layer (not shown) having a thickness of about 3 μm inascending order from the side closer to the p-side ohmic electrode 26.The height H2 (see FIG. 21) of the portion located between the uppersurface of the pad electrode 28 and the lower surface of the n-type GaNsubstrate 21 is set to about 100 μm.

An n-side ohmic electrode 29 is formed on a prescribed region of theback surface of the n-type GaN substrate 21. This n-side ohmic electrode29 is an example of the “second electrode” in the present invention. Then-side ohmic electrode 29 is constituted of an Al layer (not shown)having a thickness of about 0.006 μm, a Pd layer (not shown) having athickness of about 0.01 μm and an Au layer (not shown) having athickness of about 0.3 μm in descending order from the side closer tothe n-side GaN substrate 21.

The nitride-based semiconductor laser device is mounted on the heatradiator base (submount) 31 in a junction-up state shown in FIG. 26 or ajunction-down state shown in FIG. 27. The heat radiator base 31 is anexample of the “base” in the present invention. More specifically, then-side ohmic electrode 29 is mounted on the heat radiator base 31through a junction layer 32 of solder or the like while a wire 33 a isbonded to the upper surface of the pad electrode 28 in the junction-upstate, as shown in FIG. 26. In this case, the wire 33 a can be bonded tothe central portion of the upper surface of the pad electrode 28 formedon the principal surface of the n-side cladding layer 22 whilesuppressing wire bonding on a portion of the pad electrode 28 locatedabove the ridge portion 35 formed on the noncentral portion of theprincipal surface of the n-side cladding layer 22 in the state where then-side ohmic electrode 29 is mounted on the heat radiator base 31.Therefore, no wire bonding may be performed on the ends of the surfaceof the pad electrode 28, in order to prevent the portion of the padelectrode 28 located above the ridge portion 35 from wire bonding. Thus,the ends of the surface of the pad electrode 28 can be inhibited fromchipping in bonding of the wire 33 a. In the junction-down state, on theother hand, the pad electrode 28 is mounted on the heat radiator base 31through a junction layer 34 of solder or the like while a wire 33 b isbonded to the n-side ohmic electrode 29, as shown in FIG. 27. In thiscase, the device including the n-side cladding layer 22 having the ridgeportion 35 arranged inside the concave principal surface is mounted onthe heat radiator base 31 from the side of the pad electrode 28 formedon the n-side cladding layer 22, whereby the ridge portion 35 locatedinside the concave principal surface can be prevented from applicationof an impact when the device is mounted on the heat radiator base 31.

According to the second embodiment, as hereinabove described, the n-sidecladding layer 22 having the principal surface substantially inclinedwith respect to the principal surface of the n-type GaN substrate 21with the emission layer 23 formed on the principal surface is soprovided that the same can be grown with the principal surface inclinedwith respect to the principal surface of the n-type GaN substrate 21,whereby the n-side cladding layer 22 can be grown not only in adirection Y perpendicular to the principal surface of the n-type GaNsubstrate 21 but also in a direction X (horizontal direction) parallelthereto. When the defects 22 b propagated from the principal surface ofthe n-type GaN substrate 21 following growth of the n-side claddinglayer 22 propagate on the n-side cladding layer 22, therefore, thedefects 22 b of the n-side cladding layer 22 can be propagated not onlyin the direction Y perpendicular to the principal surface of the n-typeGaN substrate 21 but also in the direction X (horizontal direction)parallel thereto, whereby the defects 22 b can be further inhibited frompropagation to the principal surface of the n-side cladding layer 22 ascompared with a case where the defects 22 b of the n-side cladding layer22 are propagated only in the direction Y perpendicular to the principalsurface of the n-type GaN substrate 21. Thus, formation of the defects22 b on the principal surface of the n-side cladding layer 22 can befurther suppressed, whereby light absorption by the defects 22 b can befurther suppressed. Further, propagation of the defects 22 b to theemission layer 23 and the p-side cladding layer 24 can be so suppressedthat light absorption by the defects 22 b can be suppressed.Consequently, luminous efficiency can be further improved. In addition,formation of the defects 22 b on the principal surface of the n-sidecladding layer 22 can be further suppressed as described above, wherebythe number of nonradiative centers formed in the emission layer 23 canbe further reduced. Consequently, the threshold current can be furtherreduced.

The remaining effects of the second embodiment are similar to those ofthe aforementioned first embodiment.

FIGS. 28 to 40 are sectional views for illustrating a process offabricating the nitride-based semiconductor laser device according tothe second embodiment shown in FIG. 21. The process of fabricating thenitride-based semiconductor laser device according to the secondembodiment is now described with reference to FIGS. 21, 22, 24, 25 and28 to 40.

As shown in FIG. 28, the n-type GaN substrate 21 including the defectconcentration regions 21 a, having a width W7 (about 50 μm), arranged ina cycle W8 (about 400 μm) and the low defect density region 21 barranged between the defect concentration regions 21 a are prepared. Theprincipal surfaces of the defect concentration regions 21 a areterminated with nitrogen, so that growth species A can be inhibited fromdepositing on the principal surfaces of the defect concentration regions21 a. The misoriented angles of the n-type GaN substrate 21 toward the[1-100] and [11-20] directions are −0.15° and 0.15° respectively, forexample. The crystal orientation on the surface of the n-type GaNsubstrate 21 is the (0001) plane, while the defect concentration regions21 a are formed in the striped manner to extend in a direction along the[1-100] direction of the n-type GaN substrate 21. Then, the n-sidecladding layer 22 of n-type AlGaN is grown on the n-type GaN substrate21 by MOCVD, so that the central portion thereof has the thickness T3(about 2.3 μm) (see FIG. 21). In order to grow the n-side cladding layer22, the temperature, the gas pressure and the growth rate are set toabout 1100° C., about 5.74 Pa and about 0.32 nm/s respectively, whilethe gas flow rates are set to about 11 sccm for TMG, about 5 sccm forTMA, about 6 slm for NH₃ and about 20 sccm for GeH₄ respectively.

In this case, growth species A are inhibited from depositing on thesurfaces of the defect concentration regions 21 a serving as growthinhibiting portions according to the second embodiment as shown in FIG.38, whereby the concentration of the growth species A is increased inportions of the n-side cladding layer 22 close to the defectconcentration regions 21 a. Thus, the growth species A so easily depositon the portions of the n-side cladding layer 22 close to the defectconcentration regions 21 a that these portions are easier to grow ascompared with the central portion of the n-side cladding layer 22.Consequently, the central portion of the n-side cladding layer 22 andthe portions thereof close to the defect concentration regions 21 a areformed with different thicknesses, whereby the principal surface of then-side cladding layer 22 is substantially inclined with respect to theprincipal surface of the n-type GaN substrate 21. In this case, then-side cladding layer 22 is formed only on the low defect density region21 b in an initial growth stage, as shown in FIG. 38. Growth of then-side cladding layer 22 so progresses that the side portions of then-side cladding layer 22 have the prescribed inclination θ4, as shown inFIG. 39. Thereafter growth of the n-side cladding layer 22 furtherprogresses so that the n-side cladding layer 22 is formed up to theupper surfaces of the defect concentration regions 21 a while holdingthe prescribed inclination θ4 on the side portions thereof.

According to the second embodiment, the defects 22 b are formed in then-side cladding layer 22 in the growth process thereof continuously withthe defects 21 c of the n-type GaN substrate 21, as shown in FIG. 40. Inthis case, the n-side cladding layer 22 grows not only in the directionY perpendicular to the principal surface of the n-type GaN substrate 21but also in the direction X parallel thereto. More specifically, theside portions of the n-side cladding layer 22 outwardly grow from thestate shown in FIG. 40, as shown in FIG. 24. Further, the noncentralportions of the n-side cladding layer 32 inward beyond the side portionsinwardly grow (toward the central portion). The joint line 22 a (seeFIG. 25) is formed on the central portion of the n-side cladding layer22. The defects 22 b formed in the noncentral portions of the n-sidecladding layer 22 are bent in the horizontal direction X to disappear,as shown in FIG. 24. At the central portion of the n-side cladding layer22, on the other hand, the defects 22 b propagate to the surface of then-side cladding layer 22 without disappearing, due to a small growthcomponent in the direction X parallel to the surface of the n-type GaNsubstrate 21.

As shown in FIG. 29, the emission layer 23 is grown to cover the n-sidecladding layer 22. In order to grow this emission layer 23, the threewell layers 23 d of InGaN each having the thickness of about 0.003 μmand the three barrier layers 23 e of InGaN each having the thickness ofabout 0.02 μm are alternately grown as shown in FIG. 22 for forming amultilayer film of the MQW structure, thereby forming the active layer23 a constituted of the MQW structure multilayer film formed by thethree well layers 23 d and the three barrier layers 23 e. In order togrow this active layer 23 a, the temperature, the gas pressure and thegrowth rate are set to about 850° C., about 5.74 Pa and about 0.11 nm/srespectively, while the gas flow rates are set to about 75 sccm for TEG,about 230 sccm for TMI and about 8 slm for NH₃ respectively. Then, thelight guide layer 23 b of InGaN having the thickness of about 0.1 μm andthe cap layer 23 c of AlGaN having the thickness of about 0.02 μm aregrown on the active layer 23 a of InGaN having the thickness of about0.07 μm. In order to grow the light guide layer 23 b, the temperature,the gas pressure and the growth rate are set to about 860° C., about5.74 Pa and about 0.11 nm/s respectively, while the gas flow rates areset to about 75 sccm for TEG, about 30 sccm for TMI and about 8 slm forNH₃ respectively. In order to grow the cap layer 23 c, further, thetemperature, the gas pressure and the growth rate are set to about 1100°C., about 5.74 Pa and about 0.32 nm/s respectively, while the gas flowrates are set to about 20 sccm for TMG, about 250 sccm for TMA and about8 slm for NH₃ respectively. Thereafter the p-side cladding layer 24 ofAlGaN having a thickness of about 0.4 μm is grown on the surface of theemission layer 23. In order to grow the p-side cladding layer 24, thetemperature, the gas pressure and the growth rate are set to about 1100°C., about 5.74 Pa and about 0.35 nm/s respectively, while the gas flowrates are set to about 11 sccm for TMG, about 5 sccm for TMA, about 6slm for NH₃ and about 20 sccm for Cp₂Mg respectively. Thereafter thecontact layer 25 of InGaN having the thickness of about 0.003 μm isgrown on the surface of the p-side cladding layer 24. In order to growthe contact layer 25, the temperature, the gas pressure and the growthrate are set to about 850° C., about 5.74 Pa and about 0.11 nm/srespectively, while the gas flow rates are set to about 75 sccm for TEG,about 100 sccm for TMI and about 8 slm for NH₃ respectively.

As shown in FIG. 30, the Pt layer (not shown) having the thickness ofabout 0.001 μm and the Pd layer (not shown) having the thickness ofabout 0.01 μm are thereafter successively formed on the contact layer 25by vacuum evaporation or the like, thereby forming the p-side ohmicelectrode 26 consisting of the Pt and Pd layers. An SiO₂ film 36 havinga thickness of about 0.24 μm is formed on the surface of the p-sideohmic electrode 26 by plasma CVD. A striped resist film 37, having awidth of about 1.5 μm, extending in the cavity direction is formed on aregion (inward beyond the end of one of the defect concentration regions21 a by W6 (about 130 μm)) of the p-side ohmic electrode 26 for formingthe ridge portion 35 (see FIG. 21).

As shown in FIG. 31, prescribed regions of the SiO₂ film 36 and thep-side ohmic electrode 26 are removed by RIE with CF₄ gas through theresist film 37 serving as a mask. Then, the resist film 37 is removed.

As shown in FIG. 32, prescribed regions between the upper surface of thecontact layer 25 and an intermediate portion of the p-side claddinglayer 24 (having a depth of about 150 nm from the upper surface of theactive layer 23 a) are removed by RIE with Cl₂ gas through the SiO₂ film36 serving as a mask, thereby forming the ridge portion 35 consisting ofthe jut portion 24 a of the p-side cladding layer 24 and the contactlayer 25. Thereafter the SiO₂ film 36 is removed.

As shown in FIG. 33, the SiO₂ film 27 having the thickness of about 0.2μm is formed by plasma CVD to cover the overall surface. A resist film38 is applied to cover the SiO₂ film 27. Then, the resist film 38 ispartially removed by oxygen plasma etching, to expose a portion of theSiO₂ film 27 located on the ridge portion 35. Thereafter the portion ofthe SiO₂ film 27 located on the ridge portion 35 is removed by RIE withCF₄ gas through the resist film 38 serving as a mask, thereby formingthe current blocking layer consisting of the SiO₂ film 27 having a shapeshown in FIG. 34. Thereafter the resist film 38 is removed.

As shown in FIG. 35, resist films 39 are formed on regions other thanthat for forming the pad electrode 28, and the Ti layer (not shown)having the thickness of about 0.1 μm, the Pd layer (not shown) havingthe thickness of about 0.2 μm and the Au layer (not shown) having thethickness of about 3 μm are formed in this order by vacuum evaporationor the like, thereby forming the pad electrode 28. Thereafter the resistfilms 39 are removed, thereby forming the pad electrode 28 constitutedof the patterned Ti, Pd and Au layers as shown in FIG. 36. Thereafterthe lower surface of the n-type GaN substrate 21 is polished, so thatthe height H2 (see FIG. 21) of the portion located between the uppersurface of the pad electrode 28 and the lower surface of the n-type GaNsubstrate 21 is about 100 μm.

As shown in FIG. 37, the Al layer (not shown) having the thickness ofabout 0.006 μm, the Pd layer (not shown) having the thickness of about0.01 μm and the Au layer (not shown) having the thickness of about 0.3μm are formed in this order on the prescribed region of the back surfaceof the n-type GaN substrate 21 by vacuum evaporation or the like,thereby forming the n-side ohmic electrode 29 consisting of the Al, Pdand Au layers. The n-type GaN substrate 21 is divided into each device,thereby forming the nitride-based semiconductor laser device accordingto the second embodiment shown in FIG. 21.

An experiment conducted on Examples 1 to 3 and comparative example 1 forconfirming effects of the aforementioned nitride-based semiconductorlaser device according to the second embodiment in relation to thresholdcurrent and luminous efficiency is now described. In this confirmatoryexperiment, a nitride-based semiconductor laser device according toExample 1 provided with an n-type GaN substrate 21 having misorientedangles of 0° and 0.3° toward the [1-100] and [11-20] directionsrespectively, a nitride-based semiconductor laser device according toExample 2 provided with an n-type GaN substrate 21 having misorientedangles of −0.15° and 0.15° toward the [1-100] and [11-20] directionsrespectively and a nitride-based semiconductor laser device according toExample 3 provided with an n-type GaN substrate 21 having misorientedangles of −0.2° and 0.1° toward the [1-100] and [11-20] directionsrespectively were prepared in practice through a process similar to thatin the aforementioned second embodiment. Further, a nitride-basedsemiconductor laser device according to comparative example 1 wasprepared with an n-type GaN substrate 21 having misoriented angles of−0.3° and 0° toward the [1-100] and [11-20] directions respectively. Thestructure of the n-type GaN substrate 21 of the nitride-basedsemiconductor laser device according to comparative example 1 wassimilar to those of the nitride-based semiconductor laser devicesaccording to Examples 1 to 3 except the aforementioned misorientedangles. Then, inclinations of the principal surfaces (upper surfaces) ofn-side cladding layers 22, threshold currents and operating currents inoperation at 60 mA were measured in the aforementioned nitride-basedsemiconductor laser devices according to Examples 1 to 3 and comparativeexample 1. In each nitride-based semiconductor laser device, theinclination of the principal surface (upper surface) of the n-sidecladding layer 22 was measured on the upper surface of a portion of then-side cladding layer 22 inward beyond the end of a defect concentrationregion 21 a by about 130 μm with respect to the principal surface (uppersurface) of the n-type GaN substrate 21. Table 1 and FIGS. 41 and 42show the results of this experiment respectively.

TABLE 1 Misoriented angle Misoriented angle (°) toward (°) toward[1-100] Direction [11-20] Direction Inclination(°) Example 1 0 0.3 0.3Example 2 −0.15 0.15 0.2 Example 3 −0.2 0.1 0.1 Comparative −0.3 0 0Example 1

Referring to Table 1, it has been proved that the inclination of theupper surface of the n-side cladding layer 22 approaches 0° as theabsolute value of the misoriented angle of the n-type GaN substrate 21toward the [1-100] direction is increased. More specifically, theinclination of the upper surface of the n-side cladding layer 22 wasabout 0.3° in the nitride-based semiconductor laser device according toExample 1 provided with the n-type GaN substrate 21 having themisoriented angles of 0° and 0.3° toward the [1-100] and [11-20]directions respectively. The inclination of the upper surface of then-side cladding layer 22 was about 0.2° in the nitride-basedsemiconductor laser device according to Example 2 provided with then-type GaN substrate 21 having the misoriented angles of −0.15° and0.15° toward the [1-100] and [11-20] directions respectively. Further,the inclination of the upper surface of the n-side cladding layer 22 wasabout 0.1° in the nitride-based semiconductor laser device according toExample 3 provided with the n-type GaN substrate 21 having themisoriented angles of −0.2° and 0.1° toward the [1-100] and [11-20]directions respectively. In the nitride-based semiconductor laser deviceaccording to comparative example 1 provided with the n-type GaNsubstrate 21 having the misoriented angles of −0.3° and 0° toward the[1-100] and [11-20] directions respectively, on the other hand, theinclination of the upper surface of the n-side cladding layer 22 wasabout 0°.

Referring to FIG. 41, it has also been proved that the threshold currentis reduced and the luminous efficiency is improved as the inclination ofthe upper surface of the n-side cladding layer 22 is increased. Morespecifically, the threshold current of the nitride-based semiconductorlaser device according to Example 1 having the inclination of 0.3° wasabout 32 mA. The threshold current of the nitride-based semiconductorlaser device according to Example 2 having the inclination of 0.2° wasabout 32 mA. Further, the threshold current of the nitride-basedsemiconductor laser device according to Example 3 having the inclinationof 0.1° was about 43 mA. On the other hand, the threshold current of thenitride-based semiconductor laser device according to comparativeexample 1 having the inclination of 0° was about 50 mA. As theinclination is increased, a growth component of the n-side claddinglayer 22 in a direction parallel to the surface of the n-type GaNsubstrate 21 is so increased as to increase a propagation component fordefects 22 b in the direction parallel to the surface of the n-type GaNsubstrate 21. Thus, the defects 22 b so easily disappear as to reducethe number of nonradiative centers formed by the defects 22 b. Thethreshold current is conceivably reduced as a result. The thresholdcurrent is remarkably increased when the inclination is around 0°, andhence the inclination is preferably increased. Therefore, the absolutevalue of the misoriented angle toward the [1-100] direction ispreferably reduced, and the misoriented angle toward the [1-100]direction is preferably −0.25° to 0.25° from the results of theaforementioned Table 1.

Referring to FIG. 42, it has further been proved that the operatingvoltage is increased as the inclination of the upper surface of then-side cladding layer 22 is increased. More specifically, the operatingvoltage was about 6.0 V in the nitride-based semiconductor laser deviceaccording to Example 1 having the inclination of 0.3° on the uppersurface of the n-side cladding layer 22. The operating voltage was about5.1 V in the nitride-based semiconductor laser device according toExample 2 having the inclination of 0.2° on the upper surface of then-side cladding layer 22. Further, the operating voltage was about 5.1 Vin the nitride-based semiconductor laser device according to Example 3having the inclination of 0.1° on the upper surface of the n-sidecladding layer 22. On the other hand, the operating voltage was about4.9 V in the nitride-based semiconductor laser device according tocomparative example 1 having the inclination of 0° on the upper surfaceof the n-side cladding layer 22. The operating voltage is increased asthe inclination of the upper surface of the n-side cladding layer 22 isincreased, and hence the inclination is preferably optimized with thethreshold current and the operating voltage.

When employing an n-type GaN substrate 21 having defect concentrationregions 21 a formed to extend in a direction along the [1-100]direction, a propagation component for defects 22 b in a directionparallel to the surface of the n-type GaN substrate 21 is increased anddefects 22 b on the surface of an n-side cladding layer 22 easilydisappear as compared with a case of employing an n-type GaN substrate21 having defect concentration regions 21 a formed to extend in adirection along the [11-20] direction. Therefore, an n-type GaNsubstrate 21 having defect concentration regions 21 a formed to extendin a direction along the [1-100] direction is preferably employed.

In another experiment conducted independently of the aforementionedexperiment, an inclination was reduced and the principal surface of ann-side cladding layer 22 was hardly concaved when a misoriented angle θtoward the [11-20] direction of an n-type GaN substrate 21 was around 0°(−0.05<θ<0.05). Further, a tendency to nonuniform formation ofprotuberances was observed on the principal surface of the n-sidecladding layer 22. In this case, an emission layer 23 formed on theprincipal surface of the n-side cladding layer 22 is also unevenlyformed along the protuberances, and hence light in the emission layer 23easily outgoes from the upper and lower surfaces of the emission layer23. Thus, a light confinement effect is reduced to reduce luminousefficiency. Therefore, the misoriented angle toward the [11-20]direction of the n-type GaN substrate 21 is preferably set to not morethan −0.05° or at least 0.05°.

In consideration of the aforementioned results, the misoriented anglestoward the [1-100] and [11-20] directions of the n-type GaN substrate 21are preferably in ranges shown by slant lines in FIG. 43 respectively.In other words, the misoriented angle toward the [1-100] direction ofthe n-type GaN substrate 21 is preferably set to at least −0.25° and notmore than 0.25°, while that toward the [11-20] direction of the n-typeGaN substrate 21 is preferably set to not more than −0.05° or at least0.05°.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

For example, while a nitride-based semiconductor substrate (n-type GaNsubstrate) is employed as the semiconductor substrate in each of theaforementioned embodiments, the present invention is not restricted tothis but a semiconductor substrate other than the nitride-basedsemiconductor substrate may alternatively be employed.

While the nitride-based semiconductor laser device is provided with twogrowth inhibiting portions holding an element forming region thereof ineach of the aforementioned embodiments, the present invention is notrestricted to this but only a single growth inhibiting portion mayalternatively be provided on a region other than the element formingregion of the nitride-based semiconductor laser device. Referring toFIG. 37, for example, a nitride-based semiconductor laser device havinga width of about 200 μm may be formed by forming another ridge portionidentical to the ridge portion 35 on a portion inward beyond the otherdefect concentration region 21 a by about 160 μm in addition to theridge portion 35 and thereafter dividing the n-type GaN substrate 21into each device along the central portions of the defect concentrationregions 21 a and the low defect density region 21 b.

While the n-side cladding layer included in the semiconductor elementlayers is concavely formed in each of the aforementioned embodiments,the present invention is not restricted to this but the n-side claddinglayer may alternatively be so formed as to have an inclined uppersurface (principal surface) of a shape other than the concave shape.Further alternatively, a semiconductor element layer other than then-side cladding layer may be so formed as to have an inclined uppersurface (principal surface).

1-19. (canceled)
 20. A semiconductor laser device comprising: asemiconductor substrate having a principal surface; a semiconductorelement layer, formed on said principal surface of said semiconductorsubstrate, having a principal surface substantially inclined withrespect to said principal surface of said semiconductor substrate andincluding an emission layer; and a growth inhibiting portion arranged ona prescribed region of said principal surface of said semiconductorsubstrate, wherein said growth inhibiting portion includes a defectconcentration region, further comprising a projection portionfunctioning as a current path toward said emission layer, wherein saidprojection portion is formed on a noncentral portion of said principalsurface of said semiconductor element layer.
 21. The semiconductor laserdevice according to claim 20, wherein the surface of said defectconcentration region is terminated with nitrogen.
 22. The semiconductorlaser device according to claim 20, wherein said growth inhibitingportion is so provided as to extend along the <1-100> direction of saidsemiconductor substrate.
 23. The semiconductor laser device according toclaim 20, wherein said growth inhibiting portion includes a first growthinhibiting portion and a second growth inhibiting portion arranged onsaid principal surface of said semiconductor substrate at a prescribedinterval, and said semiconductor element layer is formed between saidfirst growth inhibiting portion and said second growth inhibitingportion, while said principal surface of said semiconductor elementlayer is concaved.
 24. The semiconductor laser device according to claim23, further comprising a first electrode formed on said principalsurface of said semiconductor element layer and a second electrodeformed on the back surface of said semiconductor substrate, so that saidfirst electrode of said semiconductor laser device is mounted on a base.25. The semiconductor laser device according to claim 23, furthercomprising a projection portion functioning as a current path towardsaid emission layer, wherein said projection portion is formed on aninclined region of said principal surface of said semiconductor elementlayer.
 26. The semiconductor laser device according to claim 25, furthercomprising a first electrode formed on said principal surface of saidsemiconductor element layer and a second electrode formed on the backsurface of said semiconductor substrate, so that said second electrodeof said semiconductor laser device is mounted on a base.
 27. Thesemiconductor laser device according to claim 23, further comprising aprojection portion functioning as a current path toward said emissionlayer, wherein the top of said projection portion is formed on aposition lower than the top of said semiconductor element layer.
 28. Thesemiconductor laser device according to claim 20, wherein themisoriented angle of said semiconductor substrate toward the <1-100>direction is at least −0.25° and not more than 0.25°.
 29. Thesemiconductor laser device according to claim 20, wherein themisoriented angle of said semiconductor substrate toward the <11-20>direction is not more than −0.05° or at least 0.05°.
 30. A semiconductorlaser device comprising: a semiconductor substrate having a principalsurface; a semiconductor element layer, formed on said principal surfaceof said semiconductor substrate, having a principal surfacesubstantially inclined with respect to said principal surface of saidsemiconductor substrate and including an emission layer; and a growthinhibiting portion arranged on a prescribed region of said principalsurface of said semiconductor substrate, wherein said growth inhibitingportion is terminated with nitrogen, further comprising a projectionportion functioning as a current path toward said emission layer,wherein said projection portion is formed on a noncentral portion ofsaid principal surface of said semiconductor element layer.
 31. A methodof fabricating a semiconductor laser device, comprising steps of:preparing a semiconductor substrate provided with at least either agrowth inhibiting portion including a defect concentration region or agrowth promoting portion on a prescribed region of the principalsurface; and growing a semiconductor element layer having a principalsurface inclined with respect to the principal surface of saidsemiconductor substrate and including an emission layer on the principalsurface of said semiconductor substrate through at least either saidgrowth inhibiting portion or said growth promoting portion; and forminga projection portion functioning as a current path toward said emissionlayer on a noncentral portion of said principal surface of saidsemiconductor element layer.
 32. The method of fabricating asemiconductor laser device according to claim 31, wherein said step ofpreparing said semiconductor substrate includes a step of preparing saidsemiconductor substrate in which the surface of said defectconcentration region is terminated with nitrogen.
 33. The method offabricating a semiconductor laser device according to claim 31, whereinsaid step of preparing said semiconductor substrate includes a step ofpreparing said semiconductor substrate including said growth inhibitingportion so provided as to extend along the <1-100> direction of saidsemiconductor substrate.
 34. The method of fabricating a semiconductorlaser device according to claim 31, wherein said step of preparing saidsemiconductor substrate includes a step of preparing said semiconductorsubstrate on which a first growth inhibiting portion and a second growthinhibiting portion of said growth inhibiting portion are arranged at aprescribed interval, and said step of growing said semiconductor elementlayer includes a step of growing said semiconductor element layer havinga concave principal surface between said first growth inhibiting portionand said second growth inhibiting portion.
 35. The method of fabricatinga semiconductor laser device according to claim 34, further comprising astep of forming a projection portion functioning as a current pathtoward said emission layer on an inclined region of said principalsurface of said semiconductor element layer.
 36. The method offabricating a semiconductor laser device according to claim 34, furthercomprising a step of forming the top of a projection portion functioningas a current path toward said emission layer on a position lower thanthe top of said semiconductor element layer.
 37. The method offabricating a semiconductor laser device according to claim 31, whereinthe misoriented angle of said semiconductor substrate toward the <11-20>direction is not more than −0.05° or at least 0.05 °.